Question: would it possible to make it optional similar to STOs?
So I could just ask to target by speed, chance to hit or size?
Yes, that is possible.
This is probably the best outcome as it allows you to direct your gunners to choose targets based on the tactical outlook. You might have knowledge about a certain NPR that might make different incoming missiles in a wave more/less desirable to shoot at.
It also gets around the whole realism/logic issue of what decision making process the gunners would follow.
Yes, but it also gives the NPR a harder decision, so AI work would be needed as well. Maybe a longer term option.
I would like to start by mentioning that STO targeting is currently a pain and I made a suggestion to improve it.
For the AI and player the default targeting option should be based on missile size because this is very likely to correlate with warhead size. A size 1 missile almost certainly cannot fit the same warhead as a size 6 or 12 missile.
The secondary sort should probably be missile speed because faster missiles have a better base to-hit chance and are somewhat likely to represent newer technology.
It probably needs some fuzzy logic so that a size 5.999 missile is not ignored due to a size 6.000 missile.*
If the warhead size of all incoming missiles is known then the targeting logic can swap to targeting by warhead size which is probably the most important stat.
I don't know if missile to-hit chance is supposed to be known but it gets shown in the logs. Missile to-hit chance can be used to reverse engineer the manoeuvrer rating and give to-hit chance against a target at any speed.
So the secondary sorting should be to-hit chance against the target, once known.
I think it would be more thorough to multiply to-hit chance and damage to get expected damage per missile, and sort by that value but it depends on whether to-hit and MR are supposed to be known in game.
This is all pretty in-depth and I'm not sure if we are really discussing the original question any more.
*Actually thinking about it you can design and build lots of different missiles by making lots of different research projects for a missile with the same stats. The research cost of this increases linearly by the number of missile types you want to field. Until they hit something the target cannot know which are more important or if they are identical. It might be necessary to treat all missiles of the same (or similar) size as having the same warhead size until demonstrated otherwise.
